1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic multi-functional peripheral or printer.
2. Description of the Related Art
It is very important for an image forming apparatus to stabilize the quality of an image to be formed. Generally, in an electrophotographic image forming apparatus, the density of an image to be formed (for example, the amount of a color material) is unstable due to variations in respective units (for example, the amount of electric charge retained by a color material) under image forming processing, and changes in installation environment (for example, temperature, humidity). Variations in sensitivity of a photoreceptor and changes in the environment for a transfer member also make the density of an image to be formed unstable.
The mainstream of a method to stabilize an image to be formed is a method to control development conditions (for example, see Japanese Laid-Open Patent Publication (Kokai) No. H09-319270) and a method to change image data (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2003-228201).
In the method to control development conditions, first, a patch image is formed on a photoreceptor or transfer member. Next, the toner density of the formed patch image is detected. Then, depending on the detected toner density, the ratio of magnetic powder to toner in a developing device is controlled.
In the method to change image data, the toner density of the formed patch image is detected similarly. Then, depending on the detected toner density, contents of a γLUT (gamma look-up table) are changed. A γLUT is a table to perform one-dimensional transformation on image data. The γLUT can decide output values (density signals 0 to 255) for inputted data (mainly, density signals 0 to 255).
A sensor for detecting the above patch image has a shutter member or cleaning member for preventing stains such as toners or dust on a window of the sensor (for example, see Japanese Laid-Open Patent Publication (Kokai) No. H05-322760).
There has been well known a technique using photocatalysis as typical method for preventing stains and dirt from being attached. Particularly, in the construction industry, a photocatalytic coating agent is used for the exterior such as external walls or window glass as well as for the interior. A photocatalytic coating agent has an effect to control propagation of various types of bacteria or mold, hence is used for an air cleaner. The agent is widely used for car coating, etc. (for example, see Japanese Laid-Open Patent Publication (Kokai) No. H11-347418).
For an image forming apparatus, many techniques using photocatalysis have been proposed. For example, a technique has been proposed to enable paper recycling by decomposing biding resin contained in toners to make toners to be detachable from paper (for example, see Japanese Laid-Open Patent Publication (Kokai) No. H11-338184).
However, the shutter member of a sensor typically opens during image formation, during which toners or stains adhere to the sensor. The adhered stains can be partially removed by the cleaning member, though repetitive cleaning firmly puts the stains on a protection film of the sensor.
The cleaning member is effective for toner having particles, large dust or paper dust to a certain extent. However, it cannot remove adhered volatile substances (silicone oil or wax components in toner, etc.) that generates in the image forming apparatus. In that case, the substances must be wiped out with ethanol by a service person or the sensor must be replaced.
However, the ethanol wiping causes turbidity phenomenon referred to as white turbidity on a transparent part such as a weak chemical-resistant protection layer or LED cover, decreasing sensor outputs and making density detection difficult. A film having a photocatalytic function can be arranged on or a coating agent can be applied for the above sensor to aim decomposition of stains. However, the light use efficiency is low in conventional states. To be more effective, a significant time is required and hence the technique has not been actually utilized.
To accelerate a photocatalytic reaction, a light source dedicated to sensor cleaning can be prepared. In that case, securement of a space and the cost to arrange a new light source may be barriers. Many light detecting devices can only detect a distance of several mm, having no spare space. Currently, no available image forming apparatus includes a light detecting device including the light source dedicated to sensor cleaning.